rivt is a highly extensible, open source program for writing and formatting engineering documents as text, HTML or PDF files (referred to as rivt docs). A rivt doc is generated from a rivt file (.py) that includes rivt markup and imports the rivtlib Python package. Multiple rivt docs may be organized and linked as a rivt report. This site is an example of an HTML rivt report.
An interface for finding public rivt files on GitHub is here and a repository of open source models and calculations, including rivt, is here.